Rechargeable lithium-ion batteries are widely used for portable battery applications and may find uses in larger size batteries for stationary and transportation applications. Lithium is a light element that is highly electropositive (−3 volts versus standard hydrogen electrode). The electropositive property may be utilized to provide a battery with a high open circuit voltage. Further, batteries based on light lithium metal or lithium-based alloy as the active anode material can provide a relatively high level of electrical energy per unit weight or per unit volume of the battery.
There are different embodiments of rechargeable lithium-ion batteries. One embodiment includes an anode comprising lithium metal or a lithium alloy within its structure or composition. This battery further comprises a non-aqueous, lithium-ion containing electrolyte and a cathode comprising, for example, LixMO2, where M is a transition metal such as cobalt nickel, or manganese. During charging of this battery element combination, lithium ions are removed from the cathode material as the oxidation state of the transition metal component (M) of the cathode increases. Lithium ions are inserted in the cathode during reduction at the cathode (cell discharging) as the oxidation state of the transition metal component is lowered. As stated, these electrochemical cells offer relatively high voltage and high energy density performance.
The electrolyte in a lithium-ion cell may be liquid, comprising a non-aqueous solvent in which solid lithium salts, such as lithium hexafluorophosphate (LiPF6), are dissolved in an organic solvent, for example ethylene carbonate or propylene carbonate.
In order to be suitable for automotive applications, lithium batteries need performance features that exceed the requirements for small-scale battery applications in consumer electronics and portable computers. For example, they must produce suitable electrical power over a wide temperature range, including quite low temperatures. Automotive applications of lithium-ion batteries would benefit from electrolyte materials contributing to such performance features.